This invention relates to apparatus for manufacturing honeycombed thermoplastic structures and, more particularly, to such apparatus comprising laterally moving oscillating groups of the elongated members that alternatively extend beyond the exit end of a fixed mouthpiece of an injection molding head to provide periodic lateral deviation of longitudinally moving strands of thermoplastic material so that they periodically engage each other to achieve a selective welding therebetween to form a honeycombed structure.
A conventional injection molding head for making thermoplastic honeycombed structures used as an insulating component of an electrical cable is disclosed in German Patent 1,099,680. With such a conventional injection molding head, longitudinally moving thermoplastic material exits from the head in strands from the exit ends of a multiplicity of nozzles in the head, and the injection direction of the strands are continuously changed by admitting oscillatory rotary movements to the individual nozzles, thus causing the various strands of thermoplastic material exiting the head to come into periodic contact with each other immediately beyond the exit end of the injection molding head.
Another priorly known injection molding head for making honeycombed thermoplastic structures is described in German DOS 1,779,330. As therein depicted, the injection molding head is provided with a fixed mouthpiece having a plurality of strand forming nozzle channels between which separate guide channels are provided for the passage of gas under pressure for periodically alternating the lateral movement of the strands exiting the strand forming nozzle channels, such guide channels being substantially parallel to the nozzle channels.
It is a principal object of the instant invention to provide an improved injection molding head of the immediately aforementioned type with the capability of controlling, with a high degree of exactness, the lateral deviation of the longitudinally moving strands of thermoplastic material. Preferably an extended after pressure is provided, avoidance of weld density problems is achieved, and high strength welds are realized.
In accordance with the teachings of the instant invention, an improved injection molding apparatus is set forth wherein such apparatus comprises an injection molding head having a fixed mouthpiece positioned at the exit end thereof. Such mouthpiece includes a plurality of strand channels extending longitudinally therethrough and a plurality of guide channels also extending longitudinally therethrough and interposed between various ones of the plurality of strand channels. Longitudinally extending through the plurality of guide channels are a plurality of elongated members alternately separated into a first and second group of such members. The first group of such elongated members are attached at one of each of their respective ends to a first distribution frame mechanism which serially connects each of such elongated members of the first group to each other. In a similar fashion, the second group of such elongated members are attached at one of each of their respective ends to a second distribution frame mechanism which serially connects each of such elongated members of the second group to each other. A drive mechanism is coupled to the first and second distribution frame mechanisms for providing recipricating displacement of such mechanisms longitudinally toward and away from each other so as to alternately extend the unattached opposite ends of the first and second groups of elongated members beyond the exit end of the fixed mouthpiece so that lateral oscillatory forces are applied to the freshly extruded thermoplastic strands formed at the exit end of the plurality of strand channels to provide a large periodic lateral deviation in the direction of adjacent strands so as to achieve an improved weld as the adjacent longitudinally moving strands are periodically deviated in their path of movement so as to come into contact with each other, resulting in longitudinally spaced welds.
In accordance with a first embodiment of the invention, the elongated members comprise a plurality of organ pipes, each slidably mounted in one of the plurality of guide channels for permitting a lateral high pressure discharge of gas or liquid to deviate the longitudinal movement of the immediately adjacent thermoplastic strands as they exit the strand channels of the fixed mouthpiece. The sequential movement of the unattached ends of the first and then the second group of organ pipes beyond the exit end of the fixed mouthpiece provides strictly controlled exit openings for a high pressure gas or liquid material in the organ pipes to escape therefrom in a lateral direction with respect to theh longitudinally moving, freshly extruded plastic strands. The oscillatory opening and closing of the exit openings of the organ pipes of each of the two groups results in high lateral forces being periodically applied to the extruded plastic strands in view of the dynamic effect of the resulting intermittent jet effect, especially in the case where warm air pressure is used as the strand deviating material in the organ pipes. Additionally, when the ends of the organ pipes extending beyond the exit end of the fixed mouthpiece are moved in a direction away from the exit end, a venturi nozzle effect is obtained, that is, an additional suction effect is realized on the sides of the strands being welded.
In a second embodiment of the instant invention, the elongated members extending through the guide channels of the injection molding head are comprised in a plurality of bundles of pretensioned spring lamellas, each having an end thereof which is extendable beyond the exit end of the fixed mouthpiece. Upon the ends of one of the groups of such bundles of lamellas being extended beyond the exit end of the fixed mouthpiece, the guide channel through which they pass no longer restrict lateral spreading and, accordingly, the extending portions of such bundles spread apart in a high thrust manner to engage in a lateral direction the thermoplastic strips exiting the immediately adjacent strip channels in a highly controlled and precise manner. The utilization of pretensioned bundles of spring lamellas permits a highly precise configuration with highly viscous plastic materials on a consistent basis. The outer spring lamellas of each bundle may consist of a layer of anti-bonding material, for instance, polytetrafluorethylene or be covered by such a material. The bunching of a plurality of thin spring lamellas into a package to define each of the elongated member is advantageous because the spring width of the released spring lamellas is rather large while the bending tension spring remains small.